Nanowire transistor with underlayer etch stops

ABSTRACT

A nanowire device of the present description may be produced with the incorporation of at least one underlayer etch stop formed during the fabrication of at least one nanowire transistor in order to assist in protecting source structures and/or drain structures from damage that may result from fabrication processes. The underlayer etch stop may prevent damage to the source structures and/or drain the structures, when the material used in the fabrication of the source structures and/or the drain structures is susceptible to being etched by the processes used in the removal of the sacrificial materials, i.e. low selectively to the source structure and/or the drain structure materials, such that potential shorting between the transistor gate electrodes and contacts formed for the source structures and/or the drain structures may be prevented.

RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 13/996,848, filed on Jun. 21, 2013, entitled “NANOWIRE TRANSISTORWITH UNDERLAYER ETCH STOPS”, which claims priority under 35 U.S.C. 371from International Application No. PCT/US2013/031964, filed on Mar. 15,2013, entitled “NANOWIRE TRANSISTOR WITH UNDERLAYER ETCH STOPS”, whichare hereby incorporated herein by reference in their entirety and forall purposes.

TECHNICAL FIELD

Embodiments of the present description generally relate to the field ofnanowire microelectronic devices, and, more particularly, to a nanowirestructure formed using at least one underlayer etch stop to preventremoval of portions of a source structure or a drain structure duringthe removal of sacrificial layers during the fabrication of nanowirechannels.

BACKGROUND

Higher performance, lower cost, increased miniaturization of integratedcircuit components, and greater packaging density of integrated circuitsare ongoing goals of the microelectronic industry for the fabrication ofmicroelectronic devices. As these goals are achieved, themicroelectronic devices scaled down, i.e. become smaller, whichincreases the need for optimal performance from each integrated circuitcomponent.

Maintaining mobility improvement and short channel control asmicroelectronic device dimensions scale down past the 15 nanometer (nm)node provides a challenge in microelectronic device fabrication.Nanowires may be used to fabricate microelectronic devices which provideimproved short channel control. For example, silicon germanium(Si_(x)Ge_(1-x)) nanowire channel structures (where x<0.5) providemobility enhancement at respectable Eg, which is suitable for use inmany conventional products which utilize higher voltage operation.Furthermore, silicon germanium (Si_(x)Ge_(1-x)) nanowire channels (wherex>0.5) provide mobility enhanced at lower Egs (suitable for low voltageproducts in the mobile/handheld domain, for example).

Many different techniques have been attempted to fabricate and sizenanowire-based device. However, improvements may still be need in thearea of fabricating reliable nanowire transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification.The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. It is understoodthat the accompanying drawings depict only several embodiments inaccordance with the present disclosure and are, therefore, not to beconsidered limiting of its scope. The disclosure will be described withadditional specificity and detail through use of the accompanyingdrawings, such that the advantages of the present disclosure can be morereadily ascertained, in which:

FIGS. 1-11 and 13-15 are oblique and side cross-sectional views of aprocess of forming a nanowire transistor, according to an embodiment ofthe present description.

FIG. 12 is a side cross-sectional view illustrating etching damage thatmay occur without an underlayer etch stop.

FIG. 16 is a flow chart of a process of fabricating a microelectronicdevice, according to an embodiment of the present description.

FIG. 17 illustrates a computing device in accordance with oneimplementation of the present description.

DESCRIPTION OF EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the claimed subject matter may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the subject matter. It is to be understood thatthe various embodiments, although different, are not necessarilymutually exclusive. For example, a particular feature, structure, orcharacteristic described herein, in connection with one embodiment, maybe implemented within other embodiments without departing from thespirit and scope of the claimed subject matter. References within thisspecification to “one embodiment” or “an embodiment” mean that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one implementationencompassed within the present description. Therefore, the use of thephrase “one embodiment” or “in an embodiment” does not necessarily referto the same embodiment. In addition, it is to be understood that thelocation or arrangement of individual elements within each disclosedembodiment may be modified without departing from the spirit and scopeof the claimed subject matter. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of thesubject matter is defined only by the appended claims, appropriatelyinterpreted, along with the full range of equivalents to which theappended claims are entitled. In the drawings, like numerals refer tothe same or similar elements or functionality throughout the severalviews, and that elements depicted therein are not necessarily to scalewith one another, rather individual elements may be enlarged or reducedin order to more easily comprehend the elements in the context of thepresent description.

In the production of nanowire transistors, a plurality of stackedchannel nanowires may be formed, which requires removing sacrificialmaterials from between channel gate material layers, known as a“nanowire release process”. The nanowire release process may includeetch-out processes, such as a dry etch, a wet etch, a combination ofoxidation and wet etch, and the like. However, these processes maycreate a risk of damage to source structures and/or drain structures ofthe nanowire transistors, when the material used in the fabrication ofthe source structures and/or the drain structures is susceptible tobeing etched by the processes used in the removal of the sacrificialmaterials, i.e. low selectively to the source structure and/or the drainstructure materials. Thus, the nanowire release process may result indamage to the source structures and/or the drain structures, which maylead to shorting between a transistor gate electrode and contacts formedfor the source structures and/or the drain structures, as will beunderstood to those skilled in the art.

Embodiments of the present description include the incorporation of atleast one underlayer etchstop formed during the fabrication of at leastone nanowire transistor in order to assist in protecting the sourcestructures and/or drain structures from damage that may result fromfabrication processes, such as those used in the nanowire releaseprocess.

FIGS. 1-11 and 13-15 illustrate methods of forming a nanowiretransistor. For the sake of conciseness and clarity, the formation of asingle nanowire transistor will be illustrated. As illustrated in FIG.1, the microelectronic substrate 110 may provided or formed from anysuitable material. In one embodiment, the microelectronic substrate 110may be a bulk substrate composed of a single crystal of a material whichmay include, but is not limited to, silicon, germanium,silicon-germanium or a III-V compound semiconductor material. In otherembodiments, the microelectronic substrate 110 may comprise asilicon-on-insulator substrate (SOI), wherein an upper insulator layercomposed of a material which may include, but is not limited to, silicondioxide, silicon nitride or silicon oxy-nitride, disposed on the bulksubstrate. Alternatively, the microelectronic substrate 110 may beformed directly from a bulk substrate and local oxidation is used toform electrically insulative portions in place of the above describedupper insulator layer.

As further shown in FIG. 1, a plurality of sacrificial material layers(illustrated as elements 122 ₁, 122 ₂, and 122 ₃) alternating with aplurality of channel material layers (illustrated as elements 124 ₁, 124₂, and 124 ₃) may be formed by any known technique, such as by epitaxialgrowth, on the microelectronic substrate 110 to form a layered stack126. In one embodiment, the sacrificial material layers 122 ₁, 122 ₂,and 122 ₃ may be silicon layers and the channel material layers 124 ₁,124 ₂, and 124 ₃ may be silicon germanium layers. In another embodiment,the sacrificial material layers 122 ₁, 122 ₂, and 122 ₃ may be silicongermanium layers and the channel material layers 124 ₁, 124 ₂, and 124 ₃may be silicon layer. Although three sacrificial material layers andthree channel material layers are shown, it is understood that anyappropriate number of sacrificial material layers and channel materiallayers may be used.

The layered stack 126 of FIG. 2 may be patterned using conventionalpatterning/etching techniques to form at least one fin structure 128, asshown in FIG. 3. For example, the layered stack 126 of FIG. 2 may beetched during a trench etch process, such as during a shallow trenchisolation (STI) process, wherein trenches 144 may be formed in themicroelectronic substrate 110 in the formation of the fin structure 128,and wherein the trenches 144 may be formed on opposing sides of the finstructures 128. As will be understood by those skilled in the art, aplurality of substantially parallel of fin structures 128 are generallyformed simultaneously.

As shown in FIG. 3, dielectric material structures 146, such as silicondioxide, may be formed or deposited within the trenches 144 proximatethe microelectronic substrate 110 to electrically separate the finstructures 128. As will be understood to those skilled in the art, theprocess of forming the dielectric material structures 146 may involve avariety of process including, but not limited to, depositing dielectricmaterial, polishing/planarizing the dielectric material, and etchingback the dielectric material to form the dielectric material structures146.

As shown in FIG. 4, spacers 160 may be formed on and across the finstructure 128 and may be disposed substantially orthogonally withrespect to the fin structure 128. In an embodiment, the spacers 160 maycomprise any material that may be selective during subsequent processingto the fin structure 128 materials, as will be discussed. As furthershown in FIG. 4, a sacrificial gate electrode material 152 may be formedwithin/between the spacers 160, and may be formed around portions of thefin structures 128 located between the spacers 160. In an embodiment,the sacrificial gate electrode material 152 may be formed aroundportions of the fin structure 128, and the spacers 160 may be on eitherside of the sacrificial gate electrode material 152. The sacrificialgate electrode material 152 may comprise any appropriate sacrificialmaterial, including, but not limited to polysilicon. As shown in FIG. 5,a portion of each fin structure 128 (external to the sacrificial gateelectrode material 152 and the spacers 160) may be removed to exposeportions 112 of the microelectronic substrate 110 and form a finstructure first end 128 ₁ and a fin structure second end 128 ₂ (the finstructure first end 128 ₁ is not specifically illustrated, but isessentially the mirror-image of the fin structure second end 128 ₂). Theportions of each fin structure 128 may be removed by any process knownin the art, including, but not limited to, a dry etching process.

Underlayer etch stop structure (shown as first underlayer etch stopstructure 130 ₁ and second underlayer etch stop structure 130 ₂) may beformed to abut the fin structure 128 on opposing ends of the finstructure 128. The first underlayer etch stop structure 130 ₁ and thesecond underlayer etch stop structure 130 ₂ may be any appropriatematerial that is selective to the sacrificial material layers 122 _(n),such that the sacrificial material layers 122 _(n) may be removedwithout removing the first underlayer etch stop structure 130 ₁ or thesecond underlay etch stop structure 130 ₂, as will be discussed. In oneembodiment, the first underlayer etch stop structure 130 ₁ and thesecond underlayer etch stop structure 130 ₂ may be a material that mayprovide a structure for the growth of an epitaxial material. In anotherembodiment of the present description, the first underlayer etch stopstructure 130 ₁ and the second underlayer etch stop structure 130 ₂ maybe the same material as the channel material layer 124 _(n). Thus, in aspecific embodiment, the first underlayer etch stop structure 130 ₁ andthe second underlayer etch stop structure 130 ₂ may be formed by theepitaxial growth of silicon or silicon germanium to match the channelmaterial layer 124 _(n). The epitaxial growth of the first underlayeretch stop structure 130 ₁ and the second underlayer etch stop structure130 ₂ may result in the first underlayer etch stop structure 130 ₁ andthe second underlayer etch stop structure 130 ₂ also forming on theexposed portion 112 of the microelectronic substrate 110, as shown.

As shown in FIG. 7, a source structure 170 may be formed adjacent thefirst underlayer etch stop structure 130 ₁, and a drain structure 180may be formed adjacent the second underlayer etch stop 130 ₂ on opposingends of the fin structure 128, such as by an epitaxial growth of siliconor silicon germanium. In an embodiment, the source structure 170 or thedrain structures 180 may be n-doped silicon for an NMOS device, or maybe p-doped silicon/silicon germanium for a PMOS device, depending on thedevice type for the particular application. Doping may be introduced inthe epitaxial process, by implant, by plasma doping, by solid sourcedoping or by other methods as are known in the art.

As shown in FIG. 8, an interlayer dielectric layer 190 may be formed onthe microelectronic substrate 110 over the source structures 170, thedrain structures 180, the sacrificial gate electrode material 152, andthe spacers 160, wherein the interlayer dielectric layer 190 may beplanarized, such as by chemical mechanical polishing, to expose thesacrificial gate electrode material 152. As shown in FIG. 9, thesacrificial gate electrode material 152 may then be removed from betweenthe spacer materials 160, such as by an etching process.

As shown in FIGS. 10 and 11 (cross-section along line 11-11 of FIG. 10),the sacrificial material layers 122 ₁, 122 ₂, and 122 ₃ (see FIG. 9) maybe selectively removed from the fin structure 128 (see FIG. 9) betweenthe channel material layers 124 ₁, 124 ₂, and 124 ₃ (see FIG. 9) to formchannel nanowires (illustrated as elements 120 ₁, 120 ₂, and 120 ₃, andmay be referred to herein collectively as “channel nanowires 120 _(n)”)extending between the source structure 170 (see FIG. 7) and the drainstructure 180 with the first underlayer etch stop structure 130 ₁between the channel nanowires 102 _(n) and the source structure 170, andthe second underlayer etch stop structure 130 ₂ between the channelnanowires 102 _(n) and the drain structure 180. As shown, the channelnanowires 120 _(n) may be aligned vertically (e.g. z-direction) andspaced apart from one another. In an embodiment, the sacrificialmaterial layers 122 ₁, 122 ₂, and 122 ₃ may be etched with a wet etchthat selectively removes the sacrificial material layers 122 ₁, 122 ₂,and 122 ₃ while not etching the channel material layers 124 ₁, 124 ₂,and 124 ₃ or the first underlayer etch stop structure 130 ₁ or thesecond underlayer etch stop structure 130 ₂. In one embodiment, whereinthe sacrificial material layers 122 ₁, 122 ₂, and 122 ₃ are silicon andthe channel material layers 124 ₁, 124 ₂, and 124 ₃, as well as thefirst underlayer etch stop structure 130 ₁ and the second underlayeretch stop 130 ₂, are silicon germanium, the wet etch may include, but isnot limited to, aqueous hydroxide chemistries, including ammoniumhydroxide and potassium hydroxide. In another embodiment, the silicongermanium may be removed, rather than the silicon, wherein the firstunderlayer etch stop structure 130 ₁ and the second underlayer etch stopstructure 130 ₂ would be silicon. The silicon germanium material layers124 _(n) may be selectively removed from the fin structure between thesilicon material layers 122 _(n). In an embodiment, the silicongermanium may be etched selectively with a wet etch that selectivelyremoves the silicon germanium while not etching the silicon with a wetetch including, but is not limited to, solution of carboxylicacid/nitric acid/hydrofluoric acid, and solutions of citric acid/nitricacid/hydrofluoric acid. In some embodiments of the invention, the samesilicon/silicon germanium stack is used to form both transistors withsilicon channel nanowires and transistors with silicon germanium channelnanowires. In another embodiment of the invention, the layering order ofthe silicon/silicon germanium stack may alternate depending on whethersilicon channel nanowires or silicon germanium channel nanowires arebeing formed.

In an embodiment, both silicon and silicon germanium channel nanowires120 _(n) may exist on the same wafer, in the same die, or on the samecircuit, for example as NMOS Si and PMOS SiGe in an inverter structure.In an embodiment with NMOS Si and PMOS SiGe in the same circuit, the Sichannel thickness (SiGe interlayer) and SiGe channel thickness (Siinterlayer) may be mutually chosen to enhance circuit performance and/orcircuit minimum operating voltage In an embodiment, the number of wireson different devices in the same circuit may be changed through an etchprocess to enhance circuit performance and/or circuit minimum operatingvoltage.

As shown in FIG. 12, without an underlayer etch stop, the removal of thesacrificial material layers 122 ₁, 122 ₂, and 122 ₃ may result in thesource structures 170 and/or the drain structure 180 being etched orotherwise damaged (shown as etch divots 132).

As shown in FIG. 13 (cross-section along line 13-13 of FIG. 10), a gatedielectric material 192 may be formed to surround the channel nanowires120 ₁, 120 ₂, and 120 ₃ between the spacers 160. In an embodiment, thegate dielectric material 192 may comprise a high k gate dielectricmaterial, wherein the dielectric constant may comprise a value greaterthan about 4. Example of high k gate dielectric materials may includebut are not limited to hafnium oxide, hafnium silicon oxide, lanthanumoxide, zirconium oxide, zirconium silicon oxide, titanium oxide,tantalum oxide, barium strontium titanium oxide, barium titanium oxide,strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandiumoxide, and lead zinc niobate. In one embodiment, the gate dielectricmaterial 192 may be formed substantially conformally around the channelnanowires 120 ₁, 120 ₂, and 120 ₃, and may form a substantiallyconformal layer on the spacers 160. The gate dielectric material 192 maybe deposited using any method well-known in the art to yield a conformallayer, such as, but not limited to, atomic layer deposition (ALD) andvarious implementations of chemical vapor deposition (CVD), such asatmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), and plasmaenhanced CVD (PECVD).

As shown in FIGS. 14 and 15 (cross-section along line 15-15 of FIG. 14),a gate electrode material 154 may then be formed around the channelnanowires 120 ₁, 120 ₂, and 120 ₃ to form a gate electrode 150 andthereby forming a multi-stacked nanowire transistor 100. The gateelectrode material 154 may comprise any appropriate conductive material,including, but not limited to, pure metal and alloys of titanium,tungsten, tantalum, aluminum, copper, ruthenium, cobalt, chromium, iron,palladium, molybdenum, manganese, vanadium, gold, silver, and niobium.Less conductive metal carbides, such as titanium carbide, zirconiumcarbide, tantalum carbide, tungsten carbide, and tungsten carbide, mayalso be used. The gate electrode material may also be made from a metalnitride, such as titanium nitride and tantalum nitride, or a conductivemetal oxide, such as ruthenium oxide. The gate electrode material mayalso include alloys with rare earths, such as terbium and dysprosium, ornoble metals such as platinum.

As shown in FIG. 14, the nanowire transistor 100 may include the atleast one at least one nanowire channel 120 ₁, 120 ₂, and 120 ₃ having afirst end 162 ₁, 162 ₂ and 162 ₃, respectively, and an opposing secondend 164 ₁, 164 ₂ and 164 ₃, respectively, and the source structure 170proximate the at least one nanowire channel first end 162 ₁, 162 ₂ and162 ₃, wherein the first underlayer etch stop structure 130 ₁ isdisposed between the source structure 130 ₁ and the at least onenanowire first end 162 ₁, 162 ₂ and 162 ₃, and the drain structureproximate 180 the at least one nanowire second end 164 ₁, 164 ₂ and 164₃, wherein the second underlayer etch stop structure 130 ₂ is disposedbetween the drain structure 180 and the at least one nanowire second end164 ₁, 164 ₂ and 164 ₃. Furthermore, the gate dielectric material 192may abut the at least one nanowire channel 120 ₁, 120 ₂, and 120 ₃between the nanowire channel first end 162 ₁, 162 ₂ and 162 ₃ and thenanowire channel second end 164 ₁, 164 ₂ and 164 ₃, respectively.Moreover, the gate electrode 150 may abut the gate dielectric material192. Still further, the gate electrode 150 may abut the first underlayeretch stop structure 130 ₁ and the second underlayer etch stop structure130 ₂.

It is understood that further processing may be conducted, such asforming trench contacts 196 to the source structure 170 and the drainstructure 180, as shown in FIG. 15.

FIG. 16 is a flow chart of a process 200 of fabricating a nanowiretransistor structure according to an embodiment of the presentdescription. As set forth in block 202, a microelectronic substrate maybe formed. A stacked layer comprising at least one sacrificial materiallayer and at least one channel material layer may be formed on themicroelectronic substrate, as set forth in block 204. At least one finstructure may be formed from the layered stack and the hardmask layer,as set forth in block 206. As set forth in block 208, at least twospacers may be formed across the fin structure. A sacrificial gateelectrode material may be formed between the at least two spacers, asset forth in block 210. As set forth in block 212, a portion of the finstructure external to the sacrificial gate electrode material and thespacers may be removed to form a fin structure first end and an opposingfin structure second end. Underlayer etch stop structures may be formedto abut the fin structure first end and the fin structure second end, asset forth in block 214. As set forth in block 216, a source structureand a drain structure may be formed to abut the underlayer etch stopstructures on opposing ends of the fin structure. As set forth in block218, an interlayer dielectric layer may be formed over the sourcestructure and the drain structure. The sacrificial gate electrodematerial may be removed from between the spacers, as set forth in block220. As set forth in block 222, the sacrificial material layers may beselectively removed from between the channel material layer to form atleast one channel nanowire. As set forth in block 224, a gate dielectricmaterial may be formed to surround the channel nanowire between thespacers. A gate electrode material may be formed on the gate dielectricmaterial, as set forth in block 226.

FIG. 17 illustrates a computing device 300 in accordance with oneimplementation of the present description. The computing device 300houses a board 302. The board 302 may include a number of components,including but not limited to a processor 304 and at least onecommunication chip 306. The processor 304 is physically and electricallycoupled to the board 302. In some implementations the at least onecommunication chip 306 is also physically and electrically coupled tothe board 302. In further implementations, the communication chip 306 ispart of the processor 304.

Depending on its applications, the computing device 300 may includeother components that may or may not be physically and electricallycoupled to the board 302. These other components include, but are notlimited to, volatile memory (e.g., DRAM), non-volatile memory (e.g.,ROM), flash memory, a graphics processor, a digital signal processor, acrypto processor, a chipset, an antenna, a display, a touchscreendisplay, a touchscreen controller, a battery, an audio codec, a videocodec, a power amplifier, a global positioning system (GPS) device, acompass, an accelerometer, a gyroscope, a speaker, a camera, and a massstorage device (such as hard disk drive, compact disk (CD), digitalversatile disk (DVD), and so forth).

The communication chip 306 enables wireless communications for thetransfer of data to and from the computing device 300. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 306 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 300 may include a plurality ofcommunication chips 306. For instance, a first communication chip 306may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 306 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 304 of the computing device 300 includes an integratedcircuit die packaged within the processor 304. In some implementationsof the present description, the integrated circuit die of the processorincludes one or more devices, such as nanowire transistors built inaccordance with implementations of the present description. The term“processor” may refer to any device or portion of a device thatprocesses electronic data from registers and/or memory to transform thatelectronic data into other electronic data that may be stored inregisters and/or memory.

The communication chip 306 also includes an integrated circuit diepackaged within the communication chip 306. In accordance with anotherimplementation of the present description, the integrated circuit die ofthe communication chip includes one or more devices, such as nanowiretransistors built in accordance with implementations of the presentdescription.

In further implementations, another component housed within thecomputing device 300 may contain an integrated circuit die that includesone or more devices, such as nanowire transistors built in accordancewith implementations of the present description.

In various implementations, the computing device 300 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 300 may be any other electronic device that processes data.

It is understood that the subject matter of the present description isnot necessarily limited to specific applications illustrated in FIGS.1-17. The subject matter may be applied to other microelectronic deviceand assembly applications, as well as any appropriate transistorapplication, as will be understood to those skilled in the art.

The following examples pertain to further embodiments, wherein Example 1is a nanowire transistor, comprising at least one nanowire channelhaving a first end, and an opposing second end; a source structureproximate the at least one nanowire first end, wherein a firstunderlayer etch stop structure is disposed between the source structureand the at least one nanowire first end; and a drain structuresproximate the at least one nanowire second end, wherein a secondunderlayer etch stop structure is disposed between the drain structureand the at least one nanowire second end.

In Example 2, the subject matter of Example 1 can optionally include agate dielectric material abutting the nanowire channel between thenanowire channel first end and the nanowire channel second end.

In Example 3, the subject matter of Example 2 can optionally include agate electrode material abutting the gate dielectric material.

In Example 4, the subject matter of Example 3 can optionally include thegate electrode material abutting the first underlayer etch stopstructure and the second underlayer etch stop structure.

In Example 5, the subject matter of any of Examples 1 to 4 canoptionally include the nanowire channel, the first underlayer etch stopstructure, and the second underlayer etch stop structure being the samematerial.

In Example 6, the subject matter of any of Examples 1 to 4 canoptionally include the nanowire channel, the first underlayer etch stopstructure, and the second underlayer etch stop structure are silicongermanium.

In Example 7, the subject matter of any of Examples 1 to 4 canoptionally include the nanowire channel, the first underlayer etch stopstructure, and the second underlayer etch stop structure are silicon.

In Example 8, the subject material of any of Examples 1 to 7 wherein theat least one nanowire channel may comprise a plurality of nanowireschannels formed above a microelectronic substrate, wherein the nanowirechannels are spaced apart from one another.

In Example 9, a method of forming a microelectronic structure maycomprises forming a fin structure on a microelectronic substrate,wherein the fin structure comprises at least one sacrificial materiallayer alternating with at least one channel material layer; forming atleast two spacers across the fin structure; forming a sacrificial gateelectrode material between the at least two spacers; removing a portionfin structure external to the sacrificial gate electrode material andthe spacers to form a fin structure first end and an opposing finstructure second end; forming underlayer etch stop structures to abutthe fin structure first end and the fin structure second end; andforming a source structure and a drain structure to abut the underlayeretch stop structures on opposing ends of the fin structure.

In Example 10, the subject matter of Example 9 may optionally includeforming an interlayer dielectric layer over the source structure and thedrain structure; removing the sacrificial gate electrode material frombetween the spacers; and selectively removing the sacrificial materiallayers between the channel material layers to form the at least onechannel nanowire.

In Example 11, the subject matter of Example 10 may optionally includeforming a gate dielectric material to surround the channel nanowirebetween the spacers; and forming a gate electrode material on the gatedielectric material.

In Example 12, the subject matter of any one of Examples 9 to 11 mayoptionally include forming the fin structure on the microelectronicsubstrate by forming a microelectronic substrate; forming a stackedlayer comprising at least one sacrificial material layer alternatingwith at least one channel material layer; and forming at least one finstructure from the layered stack.

In Example 13, the subject matter of any one of Example 9 to 12 mayoptionally include the channel material layer, the first underlayer etchstop structure, and the second underlayer etch stop structure being thesame material.

In Example 14, the subject matter of any one of Examples 9 to 12 mayoptionally include the channel material layer, the first underlayer etchstop structure, and the second underlayer etch stop structure beingsilicon germanium.

In Example 15, the subject matter of any one of Examples 9 to 12 mayoptionally include the channel material layer, the first underlayer etchstop structure, and the second underlayer etch stop structure beingsilicon.

In Example 16, a computing device may comprise a board including atleast one component, wherein the at least one component includes atleast one microelectronic structure comprising a nanowire transistorincluding at least one nanowire channel having a first end, and anopposing second end; a source structure proximate the at least onenanowire first end, wherein a first underlayer etch stop structure isdisposed between the source structure and the at least one nanowirefirst end; and a drain structures proximate the at least one nanowiresecond end, wherein a second underlayer etch stop structure is disposedbetween the drain structure and the at least one nanowire second end.

In Example 17, the subject matter of Example 16 can optionally include agate dielectric material abutting the nanowire channel between thenanowire channel first end and the nanowire channel second end.

In Example 18, the subject matter of Example 17 can optionally include agate electrode material abutting the gate dielectric material.

In Example 19, the subject matter of Example 18 can optionally includethe gate electrode material abutting the first underlayer etch stopstructure and the second underlayer etch stop structure.

In Example 20, the subject matter of any of Examples 16 to 19 canoptionally include the nanowire channel, the first underlayer etch stopstructure, and the second underlayer etch stop structure being the samematerial.

In Example 21, the subject matter of any of Examples 16 to 19 canoptionally include the nanowire channel, the first underlayer etch stopstructure, and the second underlayer etch stop structure being silicongermanium.

In Example 22, the subject matter of any of Examples 16 to 19 canoptionally include the nanowire channel, the first underlayer etch stopstructure, and the second underlayer etch stop structure being silicon.

In Example 23, the subject material of any of Examples 16 to 22 whereinthe at least one nanowire channel may comprise a plurality of nanowireschannels formed above a microelectronic substrate, wherein the nanowirechannels are spaced apart from one another.

Having thus described in detail embodiments of the present description,it is understood that the present description defined by the appendedclaims is not to be limited by particular details set forth in the abovedescription, as many apparent variations thereof are possible withoutdeparting from the spirit or scope thereof.

What is claimed is:
 1. A method of forming a microelectronic structure,comprising: forming a fin structure on a microelectronic substrate,wherein the fin structure comprises at least one sacrificial materiallayer alternating with at least one channel material layer; forming atleast two spacers across the fin structure; forming a sacrificial gateelectrode material between the at least two spacers; removing a portionfin structure external to the sacrificial gate electrode material andthe spacers to form a fin structure first end and an opposing finstructure second end; forming underlayer etch stop structures to abutthe fin structure first end and the fin structure second end; andforming a source structure and a drain structure to abut the underlayeretch stop structures on opposing ends of the fin structure.
 2. Themethod of claim 1, further including: forming an interlayer dielectriclayer over the source structure and the drain structure; removing thesacrificial gate electrode material from between the spacers; andselectively removing the sacrificial material layers between the channelmaterial layers to form the at least one channel nanowire.
 3. The methodof claim 2, further including: forming a gate dielectric material tosurround the channel nanowire between the spacers; and forming a gateelectrode material on the gate dielectric material.
 4. The method ofclaim 1, wherein forming the fin structure on the microelectronicsubstrate, wherein the fin structure comprises at least one sacrificialmaterial layer alternating with at least one channel material layer,comprises: forming a microelectronic substrate; forming a stacked layercomprising at least one sacrificial material layer alternating with atleast one channel material layer; and forming at least one fin structurefrom the layered stack.
 5. The method of claim 1, wherein the channelmaterial layer, the first underlayer etch stop structure, and the secondunderlayer etch stop structure are the same material.
 6. The method ofclaim 1, wherein the channel material layer, the first underlayer etchstop structure, and the second underlayer etch stop structure aresilicon germanium.
 7. The method of claim 1, wherein the channelmaterial layer, the first underlayer etch stop structure, and the secondunderlayer etch stop structure are silicon.